Neurotransmitter Effects on Release of Prolactin and Growth Hormone in Vitro From Pituitary Glands of the Pigeon, Columba Livia

Abstract

Single pigeon anterior pituitary glands were incubated with or without a hypothalamus in media containing various drugs. Release of prolactin and growth hormone was quantified by an electrophoretic-densitometric method. The hypothalamus stimulated release of both prolactin and growth hormone from the pituitary gland. Dopamine did not affect hormone release from pituitary glands incubated alone, but inhibited hypothalamus-stimulated release of prolactin and augmented hypothalamus-stimulated release of growth hormone in a dose-related manner. The effects of dopamine were reversed by its antagonist, pimozide. Serotonin stimulated release of prolactin and inhibited release of growth hormone from pituitary-hypothalamus co-incubations, and these effects were blocked by its antagonist, methysergide. Thyrotrophin releasing hormone (TRH) stimulated release of both hormones directly from pituitary glands incubated alone. Dopamine now inhibited TRH-stimulated release of prolactin, without affecting TRH-stimulated release of growth hormone. These results indicate that the neurotransmitters, dopamine and serotonin, affect the in-vitro release of factors from the hypothalamus which control the secretion of prolactin and growth hormone. In addition, dopamine may inhibit release of prolactin directly from the pituitary gland, but only when secretion of prolactin is high initially.

Serotonin and acetylcholine affect the release of prolactin and growth hormone from pituitary glands of domestic fowl in vitro in the presence of hypothalamic tissue

“…In addition Hall (1982) found that serotonin re¬ versed the hypothalamic stimulation of GH from pigeon pituitaries in vitro. The present results show an active inhibition of pituitary GH release by the hypothalamus when stimulated by serotonin or quipazine, suggesting that the amine stimulates the release of GH inhibiting hormone (somatostatin), which inhibits in vivo and in vitro GH secretion in the fowl (Harvey 1983 Unlike the Prl response, methysergide did not block the serotoninergic inhibition of GH release, a finding we have also previously observed in vivo (Hall et al, in press).…”

“…Dopamine may, in the pigeon, inhibit Prl release directly but it stimulates GH via the hypothalamus (Hall 1982). Serotonin stimulates Prl release indirectly via the hypothalamus and possi¬ bly directly also (Border & Chadwick 1977;Hall 1982;Harvey et al 1982). Its effects on GH in both the pigeon in vitro (Hall 1982) and the fowl in vivo (Rabbi et al 1981), are inhibitory.…”

“…Serotonin stimulates Prl release indirectly via the hypothalamus and possi¬ bly directly also (Border & Chadwick 1977;Hall 1982;Harvey et al 1982). Its effects on GH in both the pigeon in vitro (Hall 1982) and the fowl in vivo (Rabbi et al 1981), are inhibitory. Acetylcholine similarly stimulates the in vivo release of Prl (Har¬ vey et al 1982), whereas acetylcholine and a cholinergic agonist (carbochol) inhibit in vivo GH secretion (Harvey 1983).…”

Relationship between Hypothalamic Serotoninergic Activity and Prolactin and Growth Hormone Secretion in the Domestic Cockerel

“…9, 15, 19]. The effects of serotonin are mimicked by the re ceptor agonist, quipazine, and blocked by its antagonist, methysergide [9,15]. When given in vivo the precursors, ¿-tryptophan and 5-hydroxytryptophan, and the agonist, quipazine, all increased plasma prolactin and reduce plasma growth hormone in fowl, whereas the antagonists, methysergide, SQ-10631 and cyproheptadine, reverse these effects [15,37,41].…”

“…The monoamines dopamine (3,4-dihydroxyphenylethylamine), noradrenaline (3,4-dihydroxyphenylethanolamine) and serotonin (5-hydroxytryptamine), have been shown to affect the release of both pituitary hormones markedly [9,12,15,19,[30][31][32] 41], These transmitters are, however, only effective in vitro in the presence of hypotha lamic tissue [9,11,15], indicating that their primary mode of action is on the release of hypothalamic hypophysiotrophic releasing and/or release-inhibiting hormones.…”